This application is based on Japanese Patent Application Nos. 2001-232349 filed on Jul. 31, 2001, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to an apparatus for controlling a drive system for an automotive vehicle, which drive system includes a drive power source and an automatic transmission. More particularly, the invention is concerned with improvements of an apparatus arranged to feedback-control an engaging force of a frictional coupling device which is released to effect a shift-down action of the automatic transmission, concurrently with an engaging action of another frictional coupling device, during an operation of a manually operable vehicle accelerating member to drive the vehicle.
2. Discussion of Related Art
In an automotive vehicle, there is widely used an automotive transmission having a plurality of forward drive positions which have respective different speed ratios and which are selectively established by respective combinations of engaging and releasing actions of a plurality of frictional coupling devices. An automatic transmission of this type is automatically shifted up and down on the basis of suitably selected parameters such as an operating amount of an accelerator pedal and a running speed of the vehicle, and according to a predetermined relationship between a running condition of the vehicle defined by the selected parameters and the operating position to which the automatic transmission should be shifted. The predetermined relationship may be represented by a stored shift-boundary data map, as indicated in the graph of FIG. 6 by way of example. It will be understood from shift-down boundary lines indicated by broken lines in FIG. 6 that the automatic transmission is shifted down to increase the sped ratio when the vehicle running speed V is lowered or when an opening angle xcex8TH of a throttle valve (corresponding to the operating amount of the accelerator pedal) is increased. The speed ratio is a ratio of an input speed to an output speed of the automatic transmission. Some of the forward drive positions are established by concurrent engaging and releasing actions of respective two frictional coupling devices, namely, an engaging action of a first frictional coupling device and a releasing action of a second frictional coupling device, which take place concurrently with each other. When the automatic transmission is shifted by such concurrent engaging and releasing actions of the two frictional coupling devices, there may arise abnormal shifting behaviors of the frictional coupling devices, which cause a racing of a drive power source such as an engine, and a so-called xe2x80x9ctie-upxe2x80x9d behavior which causes a delayed shifting action of the automatic transmission to the selected forward drive position. The racing of the drive power source takes place when the first frictional coupling device to be released is prematurely brought to a substantially released state while the second frictional coupling device to be engaged is still in a substantially fully released state. On the other hand, the tie-up behavior takes place when the second frictional coupling device is prematurely brought to a substantially engaged state while the first frictional coupling device is still in a substantially fully engaged state. Therefore, the concurrent engaging and releasing actions of the two frictional coupling devices must be intricately controlled. JP-A-8-145157 discloses an example of controlling concurrent engaging and releasing actions of the two frictional coupling devices to effect a shift-up action of the automatic transmission to reduce the speed ratio, such that the engaging force of the second frictional coupling device to be engaged is controlled in a feedback fashion, and such that the engaging force at which the feedback control is initiated is updated by a learning compensation technique.
In a control apparatus disclosed in the above-identified publication, however, the first frictional coupling device to be released is not controlled is instantaneously released without controlling its engaging force in the process of the releasing action. This control apparatus suffers from a racing of the drive power source, which takes place when the releasing action of the first frictional coupling device and the engaging action of the second coupling device are effected to effect a shift-down action of the automatic transmission to increase the speed ratio, in response to an abrupt or rapid increase of a vehicle-operator""s required vehicle drive force to drive the vehicle. The required vehicle drive force may be represented by the operating amount of the accelerator pedal, and may reflect the operator""s desire to accelerate the vehicle. It is also noted that such a shift-down action of the automatic transmission in response to an abrupt increase of the operator""s required vehicle drive force is generally required to be completed in a relatively short time, in order to meet the operator""s desire to accelerate the vehicle. In this respect, it would be difficult to accurately feedback-control the engaging force of the first frictional coupling device in the process of its releasing action, due to a low control response of the engaging force.
The present invention was made in the light of the background art discussed above. It is therefore an object of the present invention to provide an apparatus for controlling a vehicle drive system including an automatic transmission, which apparatus prevents or minimizes a racing of a drive power source or any other drawback which may be caused by abnormal shifting behaviors of two frictional coupling devices in the process of respective concurrent engaging and releasing actions thereof to effect a shift-down action of the automatic transmission during an operation of a vehicle accelerating member to drive the vehicle.
The object indicated above may be achieved according to one aspect of this invention, which provides an apparatus for controlling a drive system of an automotive vehicle including a manually operable vehicle accelerating member, a drive power source, and an automatic transmission having a plurality of forward drive positions which have respective different speed ratios and which are selectively established by respective combinations of engaging and releasing actions of a plurality of frictional coupling devices, the apparatus comprising feedback control means operable upon a shift-down action of the automatic transmission which is effected by concurrent releasing and engaging actions of respective first and second frictional coupling devices of the plurality of frictional coupling devices, during an operation of the vehicle accelerating member to drive the automotive vehicle with the drive power source, the feedback control means feedback-controlling an engaging force of the first frictional coupling device, the apparatus being characterized by further comprising: shifting-abnormality detecting means for detecting one of a racing of the drive power source and a tie-up behavior of the first and second frictional coupling devices during the shift-down action of the automatic transmission; and learning compensation means operable upon detection of the above-indicated one of the racing and the tie-up behavior by the shifting-abnormality detecting means, for effecting learning compensation of an initial value of the engaging force of the first frictional coupling device at which a feedback control of the engaging force by the feedback control means is initiated.
The vehicle drive system control apparatus according to the first aspect of this invention describe above is arranged to feedback-control the engaging force of the first frictional coupling device which is released to effect the shift-down action during an operation of the manually operable vehicle accelerating member to drive the vehicle, and is further arranged to change the initial value of the engaging force of the first frictional coupling device (at which the feedback control of the engaging force is initiated), when a racing of the drive power source or tie-up behavior of the first and second frictional coupling devices is detected, so that the engaging force of the first frictional coupling device can be suitably controlled, irrespective of a low feedback control response of the engaging force, and the shift-down action can be achieved in a comparatively short time while preventing the engine racing and the tie-up behavior of the first and second frictional coupling devices.
The racing of the drive power source is an excessive rise of the operating speed of the drive power source while the first and second coupling devices are both placed in the released state. Upon subsequent engagement of the second frictional coupling device, there arises a considerably large amount of change of the vehicle drive force, undesirably causing a shifting shock and/or an excessively large shifting noise. On the other hand, the tie-up behavior of the first and second frictional coupling devices takes place when these two frictional coupling devices are both placed in the engaged state. The tie-up behavior undesirably causes a delay in the shift-down action, and a shifting shock due to a sudden decrease of the vehicle drive force.
As the automatic transmission, there is widely known a transmission of planetary gear type including a plurality of planetary gear sets connected to each other. As the frictional coupling devices, hydraulic frictional coupling devices operated by hydraulic actuators are suitably used. In this case, the engaging force of the first frictional coupling device can be controlled by controlling the duty ratio of a linear solenoid provided to control the hydraulic pressure to be applied to the hydraulic actuator.
For example, the automatic transmission is automatically shifted up and down on the basis of selected parameters representative of a running condition of the vehicle, such as a vehicle-operator""s required vehicle drive force (required output of the drive power source as represented by an operating amount of an accelerator pedal, or an opening angle of a throttle valve, for instance), and a running speed of the vehicle, and according to a predetermined relationship between the vehicle running condition and the operating position to which the automatic transmission should be shifted. The predetermined relationship may be represented by a stored data map, and is usually formulated such that the transmission is shifted down to increase the speed ratio, when the required vehicle drive force is increased or when the vehicle running speed is lowered. The shift-down action of the automatic transmission during which the shifting-abnormality detecting means is operated to detect the racing of the drive power source or the tie-up behavior of the first and second frictional coupling devices is a shift-down action which is effected during an operation of the vehicle accelerating member to drive the vehicle with the drive power source. This shift-down action may be a two-step shift-down action from a 4th-speed position to a 2nd-speed position, as well as an ordinary one-step shift-down action from the 4th-speed position to a 3rd-speed position, or from the 3rd-speed position to the 2nd-speed position.
The shift-down action is effected when the required vehicle drive force (required output of the drive power source) as represented by the operating amount of the vehicle accelerating member such as an accelerator pedal is increased while the vehicle is driven by the drive power source, that is, while the vehicle drive force is transmitted from the drive power source to the vehicle drive wheels. The shift-down action is effected not only when the required output of the drive power source as represented by the amount of operation of the vehicle accelerating member (accelerator pedal) by the vehicle operator, for instance, is increased, but also when the shift lever is operated by the vehicle operator to increase the vehicle drive force, and when an increase of the vehicle drive force is required to drive the vehicle on an uphill road without a considerable decrease of the running speed. The required vehicle drive force is increased when the opening angle of the throttle valve is increased automatically by an auto-cruise control apparatus while the vehicle is running on an uphill road in an auto-cruising mode, as well as when the amount of operation of the accelerator pedal by the vehicle operator is increased while the vehicle is running in a normal mode.
As the drive power source, an internal combustion engine such as a gasoline engine or a diesel engine may be suitably used. However, any other drive power source such as an electric motor may be used. The drive system may include a fluid-operated power transmitting device such as a torque converter or a fluid coupling, and a vehicle starting clutch which is selectively engaged and released. These fluid-operated power transmitting device and vehicle starting clutch are disposed between the drive power source and the automatic transmission.
The feedback control means may be arranged to feedback-control the engaging force of the first frictional coupling device on the basis of a difference between actual and target values of the input speed of the automatic transmission, such that the input speed is increased according to a predetermined rate, or in a predetermined pattern as represented by a desired curve. In this respect, the operating speed of the drive power source may be used in place of the input speed of the automatic transmission, provided the speed of the drive power source is almost equal to the input speed. The speed of the drive power source may be used as a parameter in place of the input speed, by any functional means other than the feedback control means, where appropriate. For instance, the shifting-abnormality detecting means may use the speed of the drive power source, to detect the racing of the drive power source or the tie-up behavior of the first and second frictional coupling devices, as described just below.
According to one preferred form of the first aspect of the invention, the shifting-abnormality detecting means detects the racing of the drive power source or the tie-up behavior of the first and second frictional coupling devices, on the basis of a change of an input speed of the automatic transmission in the process of the shift-down action, or a change of the operating speed of the drive power source.
According to a second preferred form of the first aspect of the invention, the learning compensation means changes the initial value of the engaging force by an amount which is determined on the basis of a difference of a time length during which an input speed of the automatic transmission changes between two predetermined values in the process of the shift-down action, with respect to a predetermined target value. In this case, too, the speed of the drive power source may be used in place of the input speed. The above-indicated time length corresponds to a rate of change of the input speed, and the above-indicated amount of change of the initial value may be a learning compensation value obtained on the basis of the above-indicated difference of the time length from the predetermined target value, which difference is obtained in the process of the shift-down action. However, the learning compensation means may be adapted to change the initial value of the engaging force by a constant amount which is suitably determined.
The above indicated above may also be achieved according to a second aspect of this invention, which provides an apparatus for controlling a drive system of an automotive vehicle including a manually operable vehicle accelerating member, a drive power source, and an automatic transmission having a plurality of forward drive positions which have respective different speed ratios and which are selectively established by respective combinations of engaging and releasing actions of a plurality of frictional coupling devices, the apparatus comprising feedback control means operable upon a shift-down action of the automatic transmission which is effected by concurrent releasing and engaging actions of respective first and second frictional coupling devices of the plurality of frictional coupling devices, during an operation of the vehicle accelerating member to drive the automotive vehicle with the drive power source, the feedback control means feedback-controlling an engaging force of the first frictional coupling device, the apparatus being characterized by further comprising: substantial synchronization determining means operable upon the shift-down action of the automatic transmission during the operation of the vehicle accelerating member, for determining whether an input speed of the automatic transmission has been increased to a threshold value close to a synchronization speed to be established after completion of the shift-down action; and pre-synchronization output reducing means operable upon determination by the substantial synchronization determining means that the input speed has been increased to the threshold value, for reducing an output of the drive power source.
The vehicle drive system control apparatus according to the second aspect of the present invention is arranged to feedback-control the engaging force of the first frictional coupling device which is released to effect the shift-down action during an operation of the manually operable vehicle accelerating member to drive the vehicle, and is further arranged to reduce the output of the drive power source when the input speed of the automatic transmission has been increased to the threshold value close to the synchronization speed. Accordingly, the shift-down action can be achieved in a relatively short time, while preventing a racing of the drive power source, irrespective of a low feedback control response of the engaging force of the first frictional coupling device.
According to a first preferred form of the second aspect of the invention, the substantial synchronization determining means determines whether the input speed of the automatic transmission has been increased to the threshold value, depending upon whether a difference of the input speed from the synchronization speed has become smaller than a predetermined amount. In this case, too, the input speed of the automatic transmission may be replaced by the speed of the drive power source.
According to a second preferred form of the second aspect of the invention, the pre-synchronization output reducing means reduces the output of the drive power source, by retarding an ignition timing of the drive power source. This form of the apparatus is effective to improve the control response, particularly where the drive power source is an internal combustion engine such as a gasoline engine. The method of reducing the output of the drive power source is desirably determined by the specific type of the drive power source. In one advantageous arrangement of the above preferred form of the second aspect of the invention, the pre-synchronization output reducing means retards the ignition timing on the basis of a running speed of the vehicle and an estimated input torque of the automatic transmission, and according to a predetermined data map or equation. In this case, the ignition timing can be intricately controlled. However, the pre-synchronization output reducing means may be arranged to reduce the output of the drive power source or retard the ignition timing, by a predetermined constant amount. The pre-synchronization output reducing means may start the reduction of the output of the drive power source, immediately after the moment of a determination by the substantial synchronization determining means that the input speed of the automatic transmission has been increased to the threshold value close to the synchronization speed. Alternatively, the pre-synchronization output reducing means starts the reduction of the output of the drive power source, a predetermined delay time after the moment of the determination by the substantial synchronization determining means. The delay time may be determined depending upon the specific manner of the determination by the substantial synchronization determining means.
According to a second preferred form of the second aspect of the invention, the vehicle drive system control apparatus further comprises: racing-abnormality detecting means for detecting a racing of the drive power source during the shift-down action of the automatic transmission during the operation of the vehicle accelerating member; and racing-abnormality output reducing means operable upon detection of the racing by the racing-abnormality detecting means, for immediately reducing an output of the drive power source. According to a third preferred form of the second aspect of the invention, the vehicle drive system control apparatus further comprises: shifting-abnormality detecting means for detecting one of a racing of the drive power source and a tie-up behavior of the first and second frictional coupling devices during the shift-down action of the automatic transmission; and learning compensation means operable upon detection of the racing or the tie-up behavior by the shifting-abnormality detecting means, for effecting learning compensation of an initial value of the engaging force of the first frictional coupling device at which a feedback control of the engaging force by the feedback control means is initiated.
The object indicated above may also be achieved according to a third aspect of this invention, which provides an apparatus for controlling a drive system of an automotive vehicle including a manually operable vehicle accelerating member, a drive power source, and an automatic transmission having a plurality of forward drive positions which have respective different speed ratios and which are selectively established by respective combinations of engaging and releasing actions of a plurality of frictional coupling devices, the apparatus comprising feedback control means operable upon a shift-down action of the automatic transmission which is effected by concurrent releasing and engaging actions of respective first and second frictional coupling devices of the plurality of frictional coupling devices, during an operation of the manually operable vehicle accelerating member to drive the automotive vehicle with the drive power source, the feedback control means feedback-controlling an engaging force of the first frictional coupling device, the apparatus being characterized by further comprising: racing-abnormality detecting means for detecting a racing of the drive power source during the shift-down action of the automatic transmission; and racing-abnormality output reducing means operable upon detection of the racing by the racing-abnormality detecting means, for immediately reducing an output of the drive power source.
The racing of the drive power source has been described above with respect to the first aspect of the invention. In the apparatus according to the third aspect of the invention, the output of the drive power source is reduced immediately after the detection of the racing. Accordingly, the racing-abnormality detecting means is required to monitor the input speed of the automatic transmission or the speed of the drive power source, for detecting the racing of the drive power source, in the process of the shift-down action. Therefore, the method of and the threshold value used for detecting the racing in the apparatus according to the third aspect of the invention may be different from those in the apparatus according to the first aspect of the invention.
The vehicle drive system control apparatus according to the third aspect of the invention is arranged to feedback-control the engaging force of the first frictional coupling device which is released to effect the shift-down action during the operation of the manually operable vehicle accelerating member, and is further arranged such that the output of the drive power source is reduced immediately after the detection of the racing of the drive power source. Accordingly, the shift-down action can be achieved in a relatively short time, while preventing the racing of the drive power source, irrespective of a low feedback control response of the hydraulic pressure.
According to a first preferred form of the third aspect of the invention, the racing-abnormality detecting means detects the racing of the drive power source, depending upon whether an input speed of the automatic transmission has become higher by more than a predetermined amount than a synchronization speed to be established after completion of the shift-down action. In this case, the input speed may be replaced by the speed of the drive power source. Further, a rate of change of the input speed of the transmission (a rate or change of the speed of the drive power source) may be used in addition to the input speed (the speed of the drive power source) per se.
According to a second preferred form of the third aspect of the invention, the racing-abnormality output reducing means reduces the output of the drive power source, by retarding an ignition timing of the drive power source. This form of the vehicle drive system control apparatus is effective to improve the control response, particularly where the drive power source is an internal combustion engine such as a gasoline engine. The method of reducing the output of the drive power source is desirably determined by the specific type of the drive power source. In one advantageous arrangement of the above-indicated preferred form of the third aspect of the invention, the racing-abnormality output reducing means is arranged to retard the ignition timing on the basis of a running speed of the vehicle and an estimated input torque of the automatic transmission, and according to a predetermined data map or equation. In this case, the ignition timing can be intricately controlled. However, the racing-abnormality output reducing means may be arranged to reduce the output of the drive power source or retard the ignition timing, by a predetermined constant amount.
According to a third preferred form of the third aspect of the invention, the apparatus further comprises: shifting-abnormality detecting means for detecting one of a racing of the drive power source and a tie-up behavior of the first and second frictional coupling devices during the shift-down action of said automatic transmission; and learning compensation means operable upon detection of the racing of the drive power source or the tie-up behavior of the shifting-abnormality detecting means, for effecting learning compensation of an initial value of the engaging force of the first frictional coupling device at which a feedback control of the engaging force by the feedback control means is initiated.